As someone said, you can find outdoor seating at most counter service locations. Rose and Crown has a nice patio, too, but seating there isn't guaranteed.
My favorite place for sitting outside and people watching is Wolfgang Puck Express in DTD Westside. It's right next to House of Blues and across from Virgin Megastore... there are always a ton of people out and about!
Beware, though. We've gone in December for the past 7 years or so, and last year is the warmest trip we've ever had. Most of the time it's pretty cold!!!!
In AK, all of Flame Tree BBQ's seating is outdoors, and Pizzafari has a nice little courtyard in the front, and a few tables out back, where it's quieter. All of the Norway Bakery's seating is outdoors, and I love the little courtyard to the right of Tangerine Cafe (close to potties, too!)
Ah, one of my nicest memories was having lunch on the patio at the Brown Derby at MGM (Excuse, me "Disney Stuidios"). A lovely cobb salad, cola and a piece of grapefruit cake, while people watching. It was great! (And I was with my sister, who I never thought would come to WDW with me in a million years...so sharing it with her was special too!) It was the first week in January and a beautiful day